In the wireless communications arena, an incumbent user is generally defined as any existing user of frequency spectrum. Such users may be considered as licensed, primary, secondary or unlicensed users of a frequency band. Cognitive radio is a paradigm for wireless communication in which either a network or a wireless node changes its transmission or reception parameters to communicate efficiently and utilize spectrum on a secondary basis without interfering with the incumbent users of a frequency band. This alteration of parameters is based on the active monitoring of several factors in the external and internal radio environment, such as radio frequency spectrum usage, user behavior and network state.
Regulatory bodies, such as the Federal Communications Commission (FCC), maintain significant amounts of information pertaining to incumbent transmitters and systems in a variety of frequency bands. These official databases contain information about each incumbent transmitter's operating parameters (e.g., effective radiated power, antenna pattern, antenna height above average terrain, transmitter location, etc.). Actual achieved incumbent receiver performance in the presence of CR interferers poses a large concern to regulators. Television Broadcasters (the primary licensees of the TV bands) have expressed great concern about the potential for CR interference to their broadcast services. There is also concern about the extent of services that can be provided by CR systems and whether these services will be acceptable to users due to the limiting regulatory environment within which CR systems are to operate. Determining maximum allowable interference levels for incumbent receivers is also a challenging task, due to the wide variety of (such as TV for example) receiver equipment providers on the market, and different operating conditions.
Accordingly, there is need to facilitate spectrum sharing between an incumbent communication system and a cognitive radio system.
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